Synthesis,stereochemistry and conformational properties of diastereomeric cyclic dipeptides containing tetrahydro-1,4-thiazine-3,5-dicarboxylic acid

The synthesis of linear dipeptides containing N-protected L-phenylalanine and (3R-cis)-tetrahydro-1,4-thiazine-3,5-dicarboxylic acid dialkyl diester residues is described. N-Deprotection of these dipeptides by hydrogenolysis on palladium afforded directly a mixture of cis and trans dioxopiperazines. The stereochemistry and the solution conformational properties of the cyclic dipeptides are determined.